Device manufacturers are challenged to deliver value and convenience to consumers by, for example, providing integrated circuits that offer quality performance. Multiple patterning is a technology developed for lithography to enhance feature density. Typically, for forming features of integrated circuits on wafers, a lithography process is used. Lithography processes involve applying a photoresist and defining patterns in the photoresist. The patterns in the patterned photoresist are first defined in a lithography mask, and are implemented either by transparent portions or by opaque portions in the lithography mask. The patterns in the patterned photoresist are then conventionally transferred to manufactured features.
With the increasing down-scaling of integrated circuits, the optical proximity effect poses a growing problem. When two separate features are too close to each other, the optical proximity effect sometimes causes the features to short each other. Multiple patterning technology has been introduced to form closely located features by using at least two masks of a double-patterning mask set. Both masks are used to expose the same photoresist in a lithography process. In each of the masks, the distances between features are increased over the distances between features in the otherwise single mask. As such, the optical proximity effect is reduced, or substantially eliminated.